The field of the invention is that of optical transmission of signals within optical networks referred to as “wavelength switching networks” or “band of wavelength switching networks”, also known as transparent networks.
In transparent networks, many factors can lead to inconsistencies between channels with different wavelengths in terms of performance, i.e. in terms of the quality of the signals received after transmission. This applies in particular to chromatic dispersion and amplification gain variation.
To remedy this problem, power balancing methods have been proposed with the intention of obtaining substantially constant performance from one channel to another.
These methods are suitable for “point to point” connections in which the channels of the same band take the same path and are therefore subjected to the same degradation. However, in the transparent networks previously cited, the channels present on the same transmission line (optical fiber) portion can come from different network portions and the signals in those channels can therefore have very different optical characteristics. This makes it difficult to balance performance between channels.
Each channel of an optical fiber can be optimized individually, of course, but this can degrade the performance of other channels in the optical fiber because they are interdependent because of gain coupling between the cascaded amplifiers of the transmission lines of the network.
Optimizing the balancing of channel performance is nevertheless possible in this type of transparent network, in theory, provided that certain parameters associated with the signals of each channel and related to their quality are available, for example the error rate, the optical signal to noise ratio (OSNR) and the power (optical power). This is rarely the case, however.
In practice, the performance of the channels on the longest path of the network is optimized at the design stage. To this end, the OSNR values associated with certain selected channels are determined at the end of the longest path, for example using optical spectrum analyzers (OSA) or dedicated equipment such as optical performance monitors (OPM), whilst maintaining the other channels at predefined power levels taking account of the characteristics of the network.
This kind of optimization is unsatisfactory for at least three reasons. First of all, only the channels that take the longest path are considered as potentially penalized and likely to require balancing of performance. Now this is true only provided that the other channels take shorter paths and have a large quality margin, which would compromise the very structure of the network. Secondly, because of its static nature, this kind of optimization cannot substitute non-optimized channels for optimized channels. This is because this would require the channels that take shorter paths to be at lower power levels, whilst using higher power levels for the more heavily penalized channels, which is not compatible with static processing. Finally, and again because of its static nature, this kind of optimization is incompatible with dynamic channel allocation and/or transmission line reconfiguration mechanisms.
Thus an object of the invention is to improve on this situation.